A Guerbet alcohol is a branched alcohol obtained through dehydration condensation of an aliphatic alcohol. A Guerbet alcohol is a useful substance that is directly used in or used as an intermediate material in the fields including a surfactant, a textile oil, a softening agent, a cosmetic product, a medical drug, a lubricating oil, and the like.
As a method for preparing a Guerbet alcohol, a method of subjecting an aliphatic alcohol to self-condensation in the presence of a strong base represented by an alkali metal hydroxide at a high temperature of 200° C. or more has been known (see, for example, Compt. Rend., 128, 511 (1899) (NPL 1)). However, the known method is not preferred in terms of the reaction efficiency due to the low reaction rate. The Guerbet reaction is such a reaction that an alcoholate is formed from a raw material alcohol and a strong base, an aldehyde is formed through dehydrogenation of the raw material alcohol with the alcoholate functioning like a catalyst, two molecules of the aldehyde undergo aldol condensation and then are dehydrated to provide an unsaturated aldehyde, and then the unsaturated aldehyde thus formed is reduced to form a Guerbet alcohol. The reason of the low reaction rate of the known method is considered to be deactivation of the strong base as a catalyst through saponification thereof with the aldehyde or the unsaturated aldehyde with water by-produced in the formation of the alcoholate or the dehydration of the aldol. Accordingly, the reaction is generally performed while removing by-produced water under solvent reflux (see, for example, JP 3-279336 A (PTL 1)).